DNA Structure and Replication

ID #2342

Is a euchromatin a 10nm fiber or a 10nm microfibril? The material that I got says it is a 10nm microfibril. and the TA says fiber and microfibril are not the same thing.

Before I answer your question about fiber vs. microfibril, I want to emphasize that euchromatin is not just 10nm fibers. Euchromatin is chromatin that is compacted to a 30nm fiber or less, so 30nm and 10nm fibers are examples of euchromatin. (Naked DNA is not technically chromatin because it is not associated with protein). Anything that is condensed greater than 30nm (but not including 30nm) is heterochromatin, so 300nm, 700nm and mitotic chromosomes are examples of heterochromatin. 
To address your question, beads on a string are 10nm FIBERS, not microfibrils. I don't know where you heard the term microfibril, but to the best of my knowledge it is not a term that is ever discussed in MCB 150. Chromatin is commonly referred to as fibers (10nm fibers, 30nm fibers, etc.) 

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